One of the most widely used olefin polymerization catalysts is currently, Ziegler-Natta catalyst supported by magnesium chloride. The magnesium chloride-supported Ziegler-Natta catalyst is a solid catalyst component normally comprised of magnesium, titanium, halogen and an electron donating organic compound. When being used in polymerization of alpha-olefin such as propylene, it may be mixed and used with an organoaluminum compound as a cocatalyst and an organosilane compound as a stereoregularity regulator, at a suitable ratio. Since supported solid catalysts for olefin polymerization are used in various commercialized polymerization processes such as slurry polymerization, bulk polymerization, gas phase polymerization and the like, they need to satisfy various requirements regarding a particle morphology such as suitable particle dimension and shape, uniform particle size distribution, minimized amount of macroparticles or microparticles and high bulk density, etc., as well as basically required properties such as high catalyst activity and stereoregularity.
For methods for improving particle morphology of a support for olefin polymerization catalyst, a recrystallization and reprecipitation method, a spray drying method, a chemical method and the like have been known in the art. Among them, a method for preparing a catalyst by using dialkoxy magnesium as a support, obtained from the reaction of magnesium and alcohol, i.e. one of the chemical methods, has been getting great attentions recently, since it is possible to provide a catalyst having significantly improved activity and providing polymers with high stereoregularity, as compared to other conventional methods. However, when using dialkoxy magnesium as a support, the particle shape, particle size distribution and bulk density thereof will directly affect the resulted catalyst and the particle characteristics of the produced polymers. Therefore, it is needed to produce a dialkoxy magnesium support having a uniform size, a spherical shape and sufficiently high bulk density, from the reaction between magnesium and alcohol. Particularly, a large amount of macroparticles deteriorate the flowability of polymers, and thus would make problems when being applied to a mass-production in plant-scale.
Various methods for preparing dialkoxy magnesium having a uniform shape have been disclosed in conventional technical literatures. U.S. Pat. Nos. 5,162,277 and 5,955,396 suggest methods for preparing a support having a size of 5-10 μm, by recrystallizing magnesium ethyl carbonate in a solution of various additives and solvent, wherein the magnesium ethyl carbonate is obtained from carboxylation of amorphous diethoxy magnesium. Further, Japanese laid-open patent publication Heisei06-87773 discloses a method for preparing spherical particles through processes of spray-drying an alcohol solution of diethoxy magnesium which has been carboxylated by carbon dioxide, and then decarboxylation thereof. However, these conventional methods require complicated processes using various raw materials and are not able to provide suitable particle size and morphology of the support, to the desired level.
In the meantime, Japanese laid-open patent publications Heisei03-74341, 04-368391 and 08-73388 provide synthetic methods of spherical or oval diethoxy magnesium through the reaction of magnesium metal with ethanol in the presence of iodine. However, in such methods for preparing diethoxy magnesium, a large amount of reaction heat and hydrogen are generated during the reaction which occurs very rapidly. Therefore, in said methods, it is difficult to regulate the reaction rate to the appropriate level, and the resulted product, diethoxy magnesium support disadvantageously comprises a great amount of microparticles or heterogeneous macroparticles formed of conglomerated particles.
When using a catalyst produced by using such support in olefin polymerization as it is, it causes problems such as polymers with excessively increased particle size, or destruction of particle shape owing to heat of polymerization, which causes serious troubles in process.